Data communication network architectures often have a layered structure designed for communication protocols, such as TCP/IP (transmission control protocol/Internet protocol), OSI (open systems interconnection) and SNA (system network architecture), which implement the protocol stack. With such layered structure, the protocols enable an entity in one host to interact with a corresponding entity at the same layer in a remote host. The TCP/IP protocol, for example, is a set of communication protocols that includes lower-layer protocols (such as TCP and IP) and upper-layer protocols for applications such as electronic mail, terminal emulation, and file transfer. TCP/IP can be used to communicate across any set of interconnected networks, LAN and WAN. The OSI reference model (also referred to as the OSI model) is an abstract description of a networking system divided into layers. Within each layer, one or more entities implement its functionality. According to the OSI model, each entity interacts directly with the layer immediately beneath it, and provides facilities for use by the layer above it.
Although the protocol stack may be different for each protocol, we generically refer to the lower protocol layers as layer-2 and layer-1, respectively. The lowest layer in the stack is layer-1 (or physical layer as it is also referred to). The physical layer provides the functional and procedural means for defining all the electrical and physical specifications for devices as well as for establishing and terminating connections to communication mediums on the network. Above it, layer-2 provides a forwarding domain in which devices such as bridges and switches operate. That is, layer-2 provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer.
For increased bandwidth and availability of communication channels between nodes (e.g., switches and stations), link aggregation or trunking is a method of grouping physical network links into a single logical link, i.e., a single transport channel (according to IEEE standard 802.3ad). With link aggregation, it is possible to increase capacity of communication channels between nodes using their Fast Ethernet and Gigabit Ethernet technology. Two or more Gigabit Ethernet connections can be grouped to increase bandwidth, and to create resilient and redundant links. Standard local area network (LAN) technology provides data rates of 10 Mbps, 100 Mbps and 1000 Mbps and, for obtaining higher capacity (e.g., 10000 Mbps) link aggregation allows grouping of 10 links; and where factors of ten (10) are excessive, link aggregation can provide intermediate rates by grouping links with different rates.
Layer-2 link aggregation can be used in various types of data communications, including transport channel, Ethernet port and the like. Layer-2 link aggregation uses special patterns or features of data traffic. Examples of such patterns are destination and source addresses such as MAC and IP addresses (MAC—media access control). These patterns can make traffic load balancing difficult to handle in layer-2 link aggregation operations, therefore making it desirable to have a better load balancing scheme.